Effective coaching facilitates athletes' success in reaching their potential in sport. Coaches possess a range of knowledge, skills and attributes that influence athletes' performance, including various intrapersonal and interpersonal qualities. The purpose of this study is to systematically review the research investigating the psychosocial functioning of Olympic coaches and its perceived effect on athlete performance. The review was conducted and reported in accordance with the PRISMA guidelines. The following databases were searched: SPORTDiscus, PsycINFO, PsycARTICLES, ScienceDirect, Scopus, Web of Knowledge, and Medline. The literature search identified 2873 studies which were screened and assessed for eligibility, with the resultant 25 eligible studies being assessed for quality of evidence using the Mixed Methods Appraisal Tool. Convergent meta-integration with thematic analysis was performed by converting quantitative and qualitative data from 207 Olympic coaches and 925 Olympic athletes into relevant themes and patterns. Three core themes of traits, states, and behaviors were identified. Within these themes, 18 traits, 28 states, and 38 behaviors were identified that were perceived to have either a facilitative, debilitative, or non-categorized effect on athlete performance. Future research will help national governing bodies and practitioners develop coach education to enhance Olympic coaching effectiveness.